Summary Geologic History Of the Rocky Mountain Region

Page One - Cenozoic Compiled by L.S. Fichter, Fall, 1994 Department of Geology James Madison University

Age Event Tectonic or Formations or Examples Descriptive History Geographic Units 5-0 my Glaciation Erosion and Creation of the modern unconformity Dissection of High Colorado piedmont, Pecos Uplifted edges of Paleozoic strata Except for the Gangplank in Plains and Rocky Valley New Mexico (e.g. Fountain, Minturn) form WY, high plains now separated prominent hogbacks (e.g. Garden of from Front Range pediment Mtn. Basins the Gods) Broad vertical Entire western U.S. including Front Range (Pikes Peak), Sangre Maximum summits rise to over uplift up to 5000 the Colorado plateau, Basin and de Cristo Mtns, and many other 14000 feet, most in Colorado 28-5 my feet Range province, Front Range of uplifts. along the front range. Miocene the Rockies Simultaneously broad graben Plus Rio Grande valley, St. Luis valley dropped, mostly behind Pliocene Park, Arkansas valley the Front Range dividing the region into mountains separated by deep valleys. Yellowstone hot Columbia River Plateau Columbia river plateau flood Lavas bury all structure and spot begins its basalts topography throughout journey Columbia plateau region Switch to mafic May correspond to North volcanism America overriding Pacific ocean rift center Invade as a variety of extrusive San Juan Mtns.; 39 Mile volcanic Widespread felsic volcanic Wide spread felsic volcanic fields and intrusives; field; Jemez and Datil volcanics; events invade Pre-Cambrian now mostly uplifted/exposed. Wind River Mtns., Yellowstone basement and Phanerozoic strata. volcanism Probably associated with east Widespread mineralization (e.g. 65-28 my dipping subducting plate. Leadville and Colorado gold Paleogene fields) Intermountain Formation of sub-summit Green River, Uinta, Wind River, Intermountain basin filling basin filling and pediment as Laramide Mtns etc basins continues through Miocene or eroded and become buried in later High Plains their own debris. deposition UNCONFORMITY Erosion of Laramide uplifts down to deep Precambrian basement Summary Geologic History of the Rocky Mountain Region Page Two - Mesozoic Compiled by L.S. Fichter, Fall, 1994 Department of Geology, James Madison University

Age Event Tectonic or Formations or Examples Descriptive History Geographic Units UNCONFORMITY Erosion of Laramide uplifts down to deep Precambrian basement FORELAND Mesaverde Gp and younger Beginning of K, widespread prograding non-marine and wedge of molasse sediments nearshore fms. Offshore Lewis and spreads eastward. Thick coals 65-45 my Pierre shale Late LARAMIDE OROGENY FOLD AND THRUST Central Large thrust belt zones spreading In many places Precambrian Cretaceous/ and Northern Rockies eastward in WY, ID, MT & into basement lifted to high Paleocene Canadian Rockies elevations and Phanerozoic sedimentary units stripped off FAULT BLOCK Southern Front Range, Sangra de Cristo, exposing PreC basement. Rockies. N-S trending normal Mosquito, Sawatch, etc. ranges faults Uplift 15-25,000 feet INTRUSIVES AND Idaho/Boulder (MO) batholiths; East dipping subduction; VOLCANICS Coast Range (Canada) batholiths continuation of Nevadan and Sevier Great Cretaceous Narrow seaway from Gulf of Foreland basin of Sevier and In the area of the western great Seaway Mexico to Arctic Ocean. Laramide orogenies; Mancose sh plains and eastward Remains active through rest of and Niabraro chalk between Cretaceous orogenies. Canadian Rockies complicated Tectonic events have shifted east Early-Mid by two or more docking terranes and broadened relative to Cretaceous beginning in the Jurassic Nevadan orogeny due to shallowing dip of subducting SEVIER OROGENY FORELAND Indianola gravels changing east- plate. ward to Mancose shale in Great Nevadan, Sevier and Laramide Cretaceous seaway orogenies all result from the FOLD AND THRUST BELT From far southeast Ne through same east dipping subduction central UT, eastern WY and zone. Orogenic pulses northwest through Alberta & BC correspond to increases in subduction rate. Interorogenic Franciscan MELANGE and Outer arc ridge and trough calm to slowing subduction rate.. Great Valley (Calif) sequence

FORELAND BASIN in Sundance sea and Morrison clastic Early Sundance sea pushed east Wyoming, Colorado and east wedge by thrusting, then overrun by subareal Morrison Late NEVADAN OROGENY FOLD AND THRUST BELT From eastern Nevada north through Canadian terranes: Stikine, Jurassic Utah and Idaho Cache Creek, Eastern Assemblages IGNEOUS: Sierra Nevada Evidence of volcanic activity batholith emplaced in eastern runs up through Canadian CA Rockies TRENCH: Franciscan Turbidite melanges of graywackes, Generated by an eastern dipping Accretionary Wedge dark mudstones, cherts, carbonates subduction zone under North America Early Arid Borderlands WEST Gypsum Springs & Sundance Widespread arid conditions Jurassic result in evaporates and large EAST: Zion Nat. Park Navajo sandstone; large scale cross wind blown dunes bedding Platform Redbeds EAST: Painted Desert/ Petrified Moenkopi, Chinle (Docum Gp of Semi-arid to arid savannahs with Forest but deposits from TX/OK), Wingate, Glen Canyon gallery forests (abndt vertebrates/ Triassic Arizona to Canada etc. giant redwoods) Marginal Marine WEST Dinwoody, Woodside Thaynes, Continental edge marine Chugwater, Nugget Summary Geologic History of the Rocky Mountain Region Page Three - Paleozoic Compiled by L.S. Fichter, Fall, 1994 Department of Geology, James Madison University

Age Event Tectonic or Formations or Examples Descriptive History Geographic Units Texas Permian West TX, NM: Delaware and Bone Springs blk sh, Capitan Reef, Final Retreat of Absaroka sea; Basin Midland Basins; El Capitan reef etc. Thick evaporite deposits exits to southwest EAST - Central Cordillera, [AZ: Supai, Hermit (deChelly) Non-marine remnants of Mexico to Idaho Coconino (Bird Spring ls to west), Ancestral Rockies to east Permian Toroweep, Kaibab] [UT: Park City grading to marine deposits in SONOMA OROGENY Gp, Phosphoria] west. (Semi)arid climates WEST - Sonomia terrane/ Golconda thrust in Nevada brings Same location/cause as Antler Havallah sequence; northern CA Havallah sequence onto craton. orogeny; Debate about & NE subduction direction UNCONFORMITY (Permian/Triassic - Progressive erosion of Ancestral Rockies; Fountain, Minturn, Hermosa, Sangra de Cristo formations) CO: Frontrangia, Uncom- Cutler/Fountain/Hermosa coarse Caused by wrenching of craton ANCESTRAL ROCKIES pahgria, Zuni uplifts (tops clastics along graben edges; along basement fracture zone; Pennsyl- (Colorado stripped down to basement) carbonates (reefs)/ evaporates in colliding South America vanian orogeny) Paradox basin between uplifts center) Rapid facies changes (Gondwana); Pangaea suturing AZ Supai (non-marine) grading to Callville ls UNCONFORMITY (Major offlap early in Absaroka) Missis- Orogenic Calm Madison/Redwall/Leadville Widespread, thick, resistant, ippian crinoidal/oolitic Limestones prominent WEST: Klamath/Sierra arc Remnants of arc in northern 8Dev. Volcanic arc develops (Roberts Mtn terrane); California and western Nevada along subduction facing either Devonian Nevada/Idaho deformation. west or east depending on model ANTLER OROGENY Roberts Mtn thrust in Nevada EAST: carbonate platform Wide, thick carbonates NM, UT, 68Dev. along continental edge CO east WY north through Canada 9 Dev thin, patchy exposures Silurian UNCONFORMITY Offlap of Tippecanoe; except for 6 Sil (Lone Mtn/Laketown/Fusselman ls) most of Cordillera exposed Ordovician Exposure of craton Only divergent margin remains Bighorn dolomite: NE, ID north A line through central Nevada across much of subaqueous into Canada and Idaho separates eastern UT: Eureka qtz. carbonates from western black region shales. UNCONFORMITY Sauk-Tippecanoe boundary; exposure of craton across much of region in lower Ordovician Sauk transgression Divergent Continental Margin 9C: Prospect/Flathead/Tapeats ss; Time transgressive onlap Cambrian across broad existing from 1.0-1.3 rifting Pioche/Wolsey/Bright Angle sh; thinning and younging east stable craton Howell/Mauve ls toward Transcontinental Arch û8C carbonates dominate across Transcontinental arch forms low region islands ûC Burgess shale in BC deposited off edge of continental shelf Summary Geologic History of the Rocky Mountain Region Page Four - Archaean and Proterozoic Compiled by L.S. Fichter, Fall, 1994 Department of Geology, James Madison University

Age Event Tectonic or Formations or Examples Descriptive History Geographic Units .6 Tillites found in the Belt series Glaciation .8-.6 Continental margin sandstones Canada Laid unconformably on Windermere and shales deposited at deformed Belt-Purcell rocks beginning of Sauk transgression. Thick tholeiite volcanics in lower part Late Proterozoic ?? Colorado, Walker-Texas, Set of NE and NW trending Lineaments of recurrent Craton Wide Olympic Wichita, Lewis & fractures in basement; minor N-S structural movement in basement Clark lineaments. lineament present between Transcontinental arch Orthogonal Date not clear and Cordilleran continental Fracture Zones margin.. 1.0-1.3 Aulacogens: Belt/Purcell, Grand Canyon Gp/ Belt Purcell, etc Belt contains 53,000 feet of Rifting Uinta Diverging continent may have been strata, largely quartzites. Unkar/Chuar Antarctica or Siberia Amargosa 1.0-1.1 Keweenawan/ Mid-continent Transcontinental Arch An aborted rifting event Abortive Rifting gravity high identified in Minn, but extending into the southwest 1.0- e.g. Pike's Peak Granite - Colorado A period of little or no evidence 1.2 bimodal peraluminous to of orogenic cycles but world 0.6-1.8 peralkaline granite, mafics, wide anorogenic bimodal anorthosites magmatism giving rise to Middle Anorogenic Proterozoic andesine-labradorite Magmatism 1.1 Rapakivi granite/ acid volcanics Nevada, Colorado anorthosites, rapakivi granites, plateau basalts, alkaline complexes, etc. Many of these 1.53- Granite intrusion into Stillwater Montana appear for the first time in earth 1.58 complex history and represent an important landmark in earth 1.6 Basalts, Rhyolites, Granites Arizona history. Many now exposed rocks formed as much as 35 km deep. 1.7 Granites Colorado

1.6-1.8 Major pieces of western US Scattered exposures from southern Rocks formed by island arc Proterozoic Crustal generated but extending Wyoming to northern Mexico; activity with associated eastward across to east coast exposures in Grand Canyon sediments coming on board from Accretion (Vishnu schist and Zoroaster the south granite) 1.8 - 2.5 Early 1.8-1.9 Suturing occurs along Trans- Wyoming/Hearne belt sutures with Beginning of consolidation of Proterozoic Suturing of Hudson Belt Superior province to east North American continental core. Extends far beyond Archean terranes Cordillera 2.7 Part of continent wide basic and Beartooth Mtns. of Montana Intruded originally as a Stillwater Complex ultrabasic dike swarm subhorizontal sheet into early PreC schists and gneisses. Some have attributed to boloid impact. >2.5 Generation of Wyoming/Hearne, Rae, and Wyoming province exposed in Microcontinents formed by early Archean Archean micro- Slave Wyoming uplifts and Black Hills subduction zones. Were probably sutured in the Archean continent terranes by arc-arc collisions.